5.14. Multiple Choice Exercises

Q-1: What should be the return type of the function convertToCelsius?

______ convertToCelsius (double fahrenheit) {
  double celsius;
  celsius = (fahrenheit - 32) * 5 / 9;
  return celsius;
}

• int

• What variable are we returning in the function, and what is the variable’s type?

• double

• The function returns celsius, which is a double.

• string

• What variable are we returning in the function, and what is the variable’s type?

• void

• Since we are returning something in the function, the function is not void.

Q-2: What would be returned by secretFunction if the input was 14?

int secretFunction (int input) {
  if (input % 2 == 0) {
    return 3 * input - 2;
  }
  else {
    if (input % 7 == 0) {
      return input;
    }
    return 2 * input + 9;
  }
  return input + 4;
}

• 14

• Although 14 is divisible by 7, take another look at the conditionals.

• 18

• The flow of code would never reach the last return statement.

• 36

• Check your order of operations!

• 37

• Take a closer look at the conditional statements.

• 40

• Since 14 is divisible by 2, the function returns two less than three times 14.

Q-3: If we wanted to create a boolean function called isPrime, which takes an int input as a parameter, which of the following would be the correct function header?

• boolean isPrime (int input) {

• In C++, use the bool keyword for a boolean.

• bool isPrime (input) {

• In a function header, the type of each variable must be specified in the parameter list.

• bool isPrime (int input) {

• This is the correct function header for the function.

• int isPrime (bool input) {

• Take a closer look at what the return type is.

Q-4: If we wrote the following function, which of the other functions below can we also legally write and add to the program?

int func (double x, bool y);

• int func (double a, bool b);

• Since this function has the same name and parameter types as the given function, it is not allowed.

• int foo (double x, bool y);

• This function has a different name from the given function, so it is allowed.

• int func (double x);

• Although this function has the same name as the given function, it has a different number of parameters, so it is allowed.

• void func (double x, bool y);

• Although this function has a different return type, its parameter list is the same as the given function, so it is not allowed.

• int func (bool y, double x);

• Although this function has the same name as the given function, its parameter list is in a different order, so it is allowed.

Q-5: What is the output of the code below?

int main() {
  bool x = 2 < 3;
  cout << x;
  cout << false;
  cout << ((1 + 4) * 4 > 24);
  cout << (23 == (32 + 2 - 11));
}

• 1001

• Since the first and last statements are true and the middle two are false, this is the correct output.

• truefalsefalsetrue

• In C++, boolean values are outputted as 0 or 1.

• 1false01

• Since the second cout statement doesn’t have quotes around the word “false”, the value of 0 is outputted.

• 0110

• Remember that if a boolean expression is true, it has a value of 1.

Q-6: What is the output of the code below?

int main() {
  bool w = !(2 * 3 == 6 || 4 - 3 > 8);
  bool x = true || 4 > 6;
  bool y = 3 != 6 - 3 && 23 >= 23;
  bool z = (4 + 9 < 15 && 3 != 4) || 2 + 5 == 7;
  cout << w << x << y << z;
}

• 0101

• Since the expressions are false, true, false, and true, the output is 0101.

• 1010

• Remember that true outputs to 1 and false outputs to 0.

• 1101

• Remember the NOT operator (!) inverts the value of a boolean.

• 0100

• Take a closer look at the order of operations.

• 0110

• Take a closer look at the expressions.

Q-7: Are there any issues with the code below?

bool isEven (int num) {
  if (num % 2 == 0) {
    return true;
  }
}

• Yes, we have to return either 0 or 1.

• Returning a 0 or 1 would be returning an int, even though booleans evaluate to 0 or 1.

• Yes, we cannot pass an int into a bool function.

• The type of variables in the parameter list do not affect the return type.

• Yes, there is no case for odd numbers.

• Since we never established an else clause, if the input was an odd number, the function would not return anything despite not being a void function.

• There are no issues with the code.

• There is an issue with the code. Can you find it?

Q-8: Are there any issues with the code below?

double Free_time (int day) {
  if (day==1||day==2||day==3||day==4) {
    cout<<"Better study on weekday!"<<endl;
    return day*0.25;
  }
  else{
    cout<<"Happy weekend"<<endl;
    return day;
  }
}

• Yes, we might not return anything.

• We have an else clause in which we return a value.

• Yes, we cannot return an entire expression like day*0.25.

• If the result of the expression is compatible with the return type we can return it.

• Yes, we are returning an int (in the else block) where as the return type is double.

• Implicit conversion from an int to double is ok in c++!

• There are no issues with the code.

• Correct! implicit conversion from int to double are ok!

Q-9: Are there any issues with the code below?

void moonWeight (double earth) {
  double moon = 0.165 * earth;
  cout << "You would weigh " << moon << " pounds on the moon." << endl;
  return moon;
}

• Yes, we cannot have cout statements in a function.

• We are allowed to use cout statements in a function.

• Yes, we cannot return anything.

• void functions do not have return values, so we cannot return moon.

• Yes, we need to return the output statement.

• void functions do not have return values.

• There are no issues with the code.

• There is an issue with the code. Can you find it?

Q-10: What is the return type of main?

• void

• What keyword do we use before main() in every program?

• bool

• What keyword do we use before main() in every program?

• double

• What keyword do we use before main() in every program?

• int

• Yes, main is supposed to return an integer, which is why programmers often return 0 at the end of main.

Q-11: What is the base case of the factorial recursive function?

int factorial (int n) {
  if (n == 0) {
    return 1;
  }
  else {
    int recurse = factorial (n-1);
    int result = n * recurse;
    return result;
  }
}

• n = 0

• When n is 0, the function returns the value 1 without making a recursive call.

• n = 1

• When n is 1, the function makes a recursive call in the else statement.

• n = -1

• n never becomes -1.

• There is no base case.

• If there was no base case, the function would recurse infinitely.

Q-12: What is printed?

void print_sequence (int n) {
  if (n == 0) {
     cout << 1;
     return;
     //we can have an empty return to a void function
  }
  else {
    cout << n << " ";
    print_sequence(n - 1);
  }
}

int main(){
    int val=6;
    print_sequence(val);
}

• 6 5 4 3 2 1 0

• Check what the base case prints.

• 6 6 6 6 6 6 1

• What value do we give the recursive call?

• 6 5 4 3 2 1

• The base case prints something!

• 6 5 4 3 2 1 1

• We print a number and decrement it till we reach 0 then we print 1.

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